1. Field of the Invention
This invention relates generally to rotation of objects, and more particularly to rotation of an object having a suspended center of gravity that lies within the rotation axis area of the object.
2. Description of the Related Art
Often times it is desirable to lift and rotate large pieces of equipment to gain access to all sides of the equipment In this regard, handling systems have been developed that lift and rotate objects such as rail cars, trailer frames, engine blocks, etc. Such handling systems include powered sling material handling systems such as a FLIP-RITE™ handling system available from ITNAC Corporation of Birdsboro, Pa. A powered sling material handling system employs continuous powered slings that are suspended from an overhead device that may be hung from a bridge crane or trolley hoist. Each of the continuous powered slings are passed over a rotating drum of the overhead device and around the object to be handled so as to enclose the suspended center of gravity of the object. The object is lifted by raising the overhead device and the attached slings that surround the device. The lifted object is then rotated by turning the rotating drums and slings of the overhead device using electric gear motors.
In the past, powered sling material handling systems have been used to suspend and rotate P3 Orion aircraft wing boxes to provide access to the lower wing surface for maintenance and repair. During such an operation, engines, leading edge, and trailing edge assembly are removed from the wing assembly prior to lifting and rotating the wing box. In this regard, FIG. 1 illustrates a wing box portion 100 of a disassembled wing assembly suspended above a horizontal floor surface 103 and rotated into vertical position using a conventional powered sling material handling system. As shown in FIG. 1, leading and trailing edge assemblies have been removed from wing box 102, and an end cap fitting is attached to the root edge 106 of wing box 100 that includes two lifting horns 108a and 108b that create two support points 109a and 109b. The distance between lifting horns 108a and 108b may be adjustable. Removal of leading and trailing edge assemblies, and installation of the end cap fitting are performed while wing box 100 rests in an upright horizontal position upon a wing support tool (not shown).
Prior to lifting wing box 100 from its horizontal position on the wing support tool, a first continuous sling 120 is passed around the body 102 of wing box 100 and around spacers or standoff devices 114a and 114b at an outboard position toward the wing tip edge 110 of the wing box 100 so that it is in position to contact the leading edge of the wing box 100 at support point 112a and to contact the trailing edge of wing box 100 at support point 112b. A second continuous sling 122 is passed around lifting horns 108a and 108b of the end cap fitting. As illustrated by the dashed hash lines in FIG. 1, support points 112a and 112b and support points 109a and 109b together define a rotation axis area 107 that encloses the suspended center of gravity 130 of wing box 100, i.e., so that the suspended center of gravity 130 stays between continuous slings 120 and 122 at all positions during rotation operations. Furthermore, the position of the suspended center of gravity is at or near the axis of rotation 190 of wing box 100. The distance between support points 109a and 109b is equal to the distance between support points 112a and 112b, support point 109a is horizontally aligned with support point 112a, and support point 109b is horizontally aligned with support point 112b. This equidistant and horizontally aligned support point configuration allows continuous slings 120 and 122 to rotate wing box 100 in an even manner or 1:1 relationship (i.e., rotation speed of continuous sling 120 is the same as the rotation speed of continuous sling 122) without inducing excess torque on the wing box.
As shown in FIG. 1, continuous slings 120 and 122 are passed around rotating drums 140 and 142 of lifting device 150 that is supported at pick point 170, e.g., by hoist. Lifting device 150 is then raised at pick point 170 in the direction of arrow 172 to lift wing box 100, still in horizontal position, from the wing support tool. Once clear of the wing box 100, now supported by continuous slings 120 and 122, is rotated by simultaneously turning rotating drums 140 and 142 of lifting device 150, e.g., as illustrated by arrows 174 and 176 to rotate leading edge of wing box 100 downward while maintaining wing box 100 in a position parallel to horizontal floor surface 103. In this manner wing box 100 may be rotated in the direction of arrow 160 through a vertical position (shown in FIG. 1) to a horizontal upside down position, i.e., so that its lower surface faces upward. Pick point 170 may be variably positioned relative to horizontal beam 151 of lifting device 150 as shown by arrows 171, i.e., so that pick point 170 may be vertically aligned with suspended center of gravity 130 as shown. This is necessary where center of gravity of beam 151 is not horizontally aligned with suspended center of gravity 130, and may be accomplished by lifting wing box 100 by a distance of about 1″ above the wing support tool and then rebalancing the suspended load by repositioning pick point 170.
Although the above-described wing rotation method using powered sling material handling systems has simplified the process of lifting and rotation of aircraft wing box portions of disassembled wing assemblies, both the moving and stationary components of the trailing edge assembly of a P3 Orion aircraft wing assembly (including stationary flap and aileron sections) are removed from the wing box prior to lifting and rotation to ensure that the suspended center of gravity of the wing box is enclosed within an area defined between the support points and lifting horns and is near the axis of rotation of the wing assembly. Otherwise, the wing box may become unstable during the lifting and/or rotation process, and/or excessive torque may be required to rotate the wing box. Removal of the entire trailing edge assembly (i.e., moving and stationary components) is a time consuming and labor intensive operation (e.g., requiring 680 man-hours of time).